In industrial settings, control systems are used to monitor and control inventories of industrial and chemical processes and the like. Typically, the control system performs these functions using field devices distributed at key locations in the industrial process coupled to the control circuitry in the control room by a process control loop. The term “field device” refers to any device that performs a function in a distributed control or process monitoring system used in the measurement, control, and monitoring of industrial processes. Typically, field devices are characterized by their ability to operate outdoors for extended periods of time, such as years. Thus, a field device is able to operate in a variety of climatological extremes, including severe temperature extremes and extremes in humidity. Moreover, field devices are able to function in the presence of significant vibration, such as vibration from adjacent machinery. Further, field devices may also operate in the presence of electromagnetic interference.
One example of a field device is a multivariable process fluid flow device, such as that sold under the trade designation Model 3051 SMV Multivariable Transmitter by Emerson Process Management of Chanhassen, Minn. Multivariable process fluid flow devices can compute mass flow rate through differential producers for liquids and gases. Generally, such computation requires measurement of the differential pressure across the differential pressure producer, as well as measurement of the static or line pressure and the temperature of the process fluid.
The general equation for calculating flow rate through a differential producer can be written as:Q=NCdEY1d2√{square root over (ρh)}where:    Q=Mass flow rate (mass/unit time)    N=Units conversion factor (units vary)    Cd=Discharge coefficient (dimensionless)    E=Velocity of approach factor (dimensionless)    Y1=Gas expansion factor (dimensionless)    d=Bore of differential producer (length)    ρ=Fluid density (mass/unit volume)    h=Differential pressure (force/unit area)
Of the terms in this expression, only the units conversion factor, which is a constant, is simple to calculate. The other terms are expressed by equations that range from relatively simple to very complex. Some of the expressions contain many terms and require the raising of numbers to non-integer powers. This is a computationally intensive operation.
It is desirable to have the process fluid flow device operate compatibly with as many types of differential producers as possible. Further, it is also desirable to provide a process fluid flow device that is able to measure flow rate for a variety of process fluids over a variety of operating conditions.
In order to accurately measure a process fluid flowing through a differential producer, not only must differential pressure, static or line pressure, and temperature be measured very accurately, but substantial information about the differential pressure producer itself and the process fluid are required. Further, some of the required information may be difficult for a technician to locate and/or extrapolate to the operating range. Thus, providing a process fluid flow device with the requisite a priori information could be extremely difficult and time consuming. Fortunately, this process is aided considerably by a software application available from Emerson Process Management, sold under the trade designation Engineering Assistant. This software application includes a database of various parameters relative to common differential pressure producers and process fluids. Thus, a technician need only couple a process fluid flow device to a computer running the software application and follow a configuration wizard that requests various pieces of information and automatically provides process fluid flow device configuration information, such as polynomial coefficients, to the process fluid flow device. One of the complexities of configuring a process fluid flow device is that data entered by the technician as well as calculations performed by the software may generate warnings or otherwise affect other parameters. For example, the fluid density may be able to be calculated appropriately in a default operating range, but if a technician indicates that the process fluid flow device will measure fluid in a range that is outside the default range, fluid density may not be able to be calculated with the requisite accuracy. Accordingly, the software may warn the user with respect to the operating range provided. Thus, while the process of guiding a technician through configuration of a process fluid flow device can generally be effected in a relatively linear fashion, the interrelatedness of the various data entered, and warnings provided, may cause the technician to wish to return to an earlier step to make a change. This can become confusing given the interrelatedness of all of the data.
A system and method that provides more user friendly configuration of a complex process fluid flow device would benefit the industrial process fluid flow field.